1. Field of the Invention
The present invention generally relates to coordinate input and detection devices and information display and input apparatuses, and more particularly to a coordinate input and detection device employed in, for instance, an optical coordinate input device, an optical coordinate detection device, or an optical touch panel and to an information display and input apparatus including such a coordinate input and detection device and an information display unit having a display, such as a large screen display unit with a touch panel, an electronic blackboard, a video conference apparatus, a large scale projection touch panel apparatus, a display-integrated tablet, or a multimedia board.
2. Description of the Related Art
Generally, in conferences or at the presentations of studies, a blackboard or a whiteboard is often employed as an information transfer medium that enables a large number of people to see the content of a study or proceedings at the same time. Recently, there has been an increased demand for an electronic blackboard, which can store and print out on papers what is written thereon.
Further, there has been developed an information display and input system that inputs a position or information to a computer in real time, which position or information is indicated or written on a touch panel on a display by a finger of an operator or a touch pen, and displays a variety of information corresponding to the indicated position or written information.
In such a system, it is necessary to detect with high accuracy an indicated position, or a touched position, on the surface of the touch panel when the inputs are made from the touch panel.
For instance, Japanese Patent No. 2678231 discloses, as a coordinate input and detection device detecting an indicated position on the surface of a touch panel, a device that has numerous optical emitters and detectors arranged in positions opposing each other on the periphery of the touch panel surface of a display screen to form a light beam matrix all over the touch panel surface so that a position where light beams are interrupted (hereinafter referred to as a light beam interruption position) by a contact of a finger or a pen with the touch panel can be detected.
Since the above-mentioned device has an advantage of achieving a high signal to noise ratio (S/N), the application of the device is extendable to a large-scale display unit. However, since the resolution of detection is proportional to a distance between each two adjacently arranged optical emitters or detectors, the device requires a large number of optical emitters and detectors to be arranged with narrow pitches so as to detect an input coordinate value with high accuracy. Therefore, the signal processing circuit of the optical emitters and detectors becomes complicated, thus increasing costs.
Japanese Laid-Open Patent Application No. 5-53717 discloses an optical two-dimensional coordinate input device that projects a light beam such as a laser beam from each of two points outside a touch panel to scan a region defined by projection angles of each light beam. According to the device, the angles of a position of a pen used exclusively for the device for retroreflecting the projected light beams are obtained from the lights reflected from the pen so as to calculate the coordinate position of the pen by applying the obtained angles to the principle of triangulation.
This coordinate input device, however, requires the pen used exclusively therefor, thus having an operational problem that an input to the device cannot be made by means of a finger or any pen other than the pen used exclusively for the device.
Japanese Laid-Open Patent Application No. 11-85376 discloses a device that has a pair of light emitting and receiving units each including a light emitting element, a light receiving element, and a polygon mirror disposed outside both corners of one side of a display panel. According to the device, the polygon mirrors are turned to scan almost all the surface of the display panel by means of two light beams. The light beams are reflected by retroreflective sheets provided on the longitudinal sides of the display panel to be detected by the light receiving elements of the above-described pair of the light emitting and receiving units so that a coordinate position is calculated by employing the principle of triangulation.
This device allows an input by means of a finger or a pen, provides a good visual recognizability, and is relatively easily enlarged in size. However, the device includes mechanical rotating parts, thus generating noises and vibrations. Therefore, the device has a difficulty in increasing detection accuracy in addition to problems of failure and durability.
The inventor of the present invention has already proposed a coordinate input and detection device that includes at least a couple of emitting means each projecting a light beam that is a parallel beam of an approximately uniform thickness in a direction perpendicular to a touch panel and has a sector shape in a direction parallel to the touch panel. According to the device, the light beams travel over a given region of the touch panel almost parallel to the surface thereof to be reflected by retroreflective sheets provided on the peripheral portion of the touch panel. The reflected lights are detected by at least a couple of intensity distribution detection means, which are optical-electrical transducers such as charge coupled devices (CCDs), so that the intensity distribution of each light is detected. The coordinate value of a position where the lights beams traveling over the given region of the touch panel are interrupted is detected by the intensity distributions of the light beams.
According to the above-described device, by interrupting a part of each light beam projected all over the given region of the touch panel by indicating a position on the surface of the touch panel by means of any indicator such as a finger or a pen, the coordinate value of the light beam interruption position is detected with high accuracy so that a desired input operation is performed. Therefore, the device dispenses with a special pen including a reflective material. Further, since the device does not employ a mechanical scanning mechanism such as a polygon mirror, the device is free of noises and vibrations to achieve good detection accuracy with fewer failures and good durability, thus eliminating all of the conventional disadvantages.
However, in order to detect the light beam interruption position with good accuracy from the intensity distributions of the light beams received by the intensity distribution detection means, each of the light beams received by the light receiving surfaces of the above-described intensity distribution detection means is required to have its amount of light approximately uniformly distributed in a direction parallel to the surface of the touch panel and perpendicular to a traveling direction of the reflected light of the light beam traveling over the given region of the touch panel.
However, the distribution of the amount of light in a direction perpendicular to the optical axis of a light-emitting diode (LED) or a laser diode (LD) employed as a light source of each light emitting means, which distribution correlates to the intensity distribution of light emission, has a non-uniform characteristic that as indicated by a curve 51 shown in FIG. 1, the amount of light is maximized around a light source 50 and decreases in proportion to a distance therefrom.
Therefore, in the case of forming, by a combination of cylindrical lenses, the light beam into the parallel beam of the approximately uniform thickness in the direction perpendicular to the touch panel and into the sector shape in the direction parallel to the touch panel, the distribution of the amount of light in the direction parallel to the surface of the touch panel particularly has a characteristic that the amount of light is maximized at the center portion of the light beam and decreases as a measurement point of the amount of light approaches each end portion of the light beam.
Therefore, a light modulation plate 60 is disposed on an optical path of the light beam projected from each light emitting means to be received by each intensity distribution detection unit 70 so that the amount of light is modulated to be uniformly distributed in the direction parallel to the surface of the touch panel.
That is, as shown in FIG. 1, a light beam 55 projected from each light emitting means (not shown) to be reflected back from the retroreflective sheet is made incident on a condenser lens (image formation lens) 71 of the intensity distribution detection unit 70 through an opening portion 60a of the light modulation plate 60. An image is formed, by the function of the condenser lens 71, on a light receiving element array 72b formed by light receiving elements arranged in a linear array on a light receiving surface 72a of a CCD 72 that is an optical-electrical transducer so that the intensity distribution of the light beam 55 is detected.
The light modulation plate 60 is stamped out from a sheet metal to have its outer shape and the opening portion 60a formed. The opening portion 60a is a slit longitudinally narrow in a spreading direction of the light beam 55 parallel to the surface of the touch panel (in a right-to-left direction or a Y-axial direction in FIG. 1), and has its width d gradually varying so as to be the widest at both end portions thereof and the narrowest at the center thereof.
Therefore, if a light beam having its amount of light distributed uniformly all over the opening portion 60a in a longitudinal direction thereof is made incident on the opening portion 60a, the amount of light of the light beam passing through the light modulation plate 60 is distributed to be minimized at the center portion of the light beam and maximized at both end portions thereof, as indicated by a curve 52 shown in FIG. 1.
However, as described above, the distribution of the amount of light of the actual light source 50 has the characteristic indicated by the curve 51 of FIG. 1. Therefore, by passing through the light modulation plate 60, the light beam can be modulated to have its amount of light distributed almost uniformly in the Y-axial direction as indicated by a broken curve 53 of FIG. 1.
The light beam 55 is made incident on the condenser lens 71 so as to be gathered at the center thereof in the Y-axial direction, and is laterally reversed to form the image on the light receiving element array 72b of the CCD 72 so that the intensity distribution of the light beam is detected. Accordingly, in this manner, an intensity distribution signal having an almost uniform level all over the light receiving element array 72b is usually detected.
Thus, by changing the shape of the opening portion 60a of the light modulation plate 60, the incident light beam can be modulated to have a desired distribution of its amount of light. Therefore, the distribution of the amount of light of the light beam 55 in the Y-axial direction can be adjusted to the characteristic of the CCD 72.
This requires a thickness D of the incident light beam 55 in a direction perpendicular to the surface of the touch panel to be thicker than a certain thickness, and the maximum value of the width d of the opening portion 60a of the light modulation plate 60 is determined based on the thickness D. If the maximum value of the width d is small, a variation in the width d is prevented from being great, thus narrowing a light modulation range. Therefore, the narrowed light modulation range, together with a limit to the dimensions of a metal mold for processing the sheet metal and a problem of processing accuracy, prevents a desired light modulation characteristic from being obtained.
However, in the above-described coordinate input and detection device, the thickness D of the sector-shaped light beam 55 projected over the surface of the touch panel is required to be as thin as possible to minimize a detectable region in the direction perpendicular to the surface of the touch panel so that a wrong detection based on an unnecessary interruption of the light beam other than an indication by means of a finger or an indication pen is prevented from being caused and that the detection accuracy of the coordinate value of a light beam interruption position is increased.
It is difficult to satisfy both of the above-described requirements. The above-described adjustment of the distribution of the amount of light of the light beam 55 incident on the light receiving surface 72a by means of the light modulation plate 60 is prevented from making sufficiently thin the thickness D of the light beam 55 in the direction perpendicular to the surface of the touch panel. Therefore, there remains the problem that a wrong detection based on an unnecessary interruption of the light beam other than an indication by means of a finger or an indication pen is caused or a sufficient detection accuracy of the coordinate value of a light beam interruption position is prevented from being obtained.